BREAKING NEWS! It seems there is evidence that cells, organelles , and all major metabolic pathways evolved from early prokaryotic cells. With us today, we have Dr Mulder here to tell us all about it.
Thanks for having me! But actually, these theories aren't new, and have been being studied over 200 years! For example, endosymbiosis, the theory that mitochondria and chloroplasts originated from prokaryotic cells, began in 1883.
There is a lot of evidence for this! For one, Mitochondria have their own cell membranes, just like a prokaryotic cell does. Each mitochondria has its own circular DNA, like a bacteria. To reproduce, mitochondria pinch in half — the same process used by bacteria.
Also, some early eukaryotes found lack these organelles! This further indicates the idea that they were originally independent prokaryotes that got engulfed.
Finally, the functions of mitochondria, cellular respiration, and chloroplasts, photosynthesis, would have been evolutionarily beneficial to these early cells. It makes sense that if they got engulfed, natural selection selected for the prokaryotes that contained them.
What about other cells and major metabolic pathways?
Great question! Well, when the first living organisms appeared, there was no oxygen so only anaerobic cells could survive. These included phototrophs which got energy from the sun, and chemoautotrophs. Eventually, cyanobacteria evolved from these early phototrophs.
These cyanobacteria slowly oxygenated the atmosphere, and as this happened, multicellular life forms began to form and evolve. These evolved into aerobic cells and microbes, and eventually into the plants and animals around us today!